在PHP中，变量赋值何时返回false？(In PHP when would a variable assignment return false?)

 什么时候PHP变量赋值返回false？ 
 
 在本回答中 ，建议使用以下代码 
 
while (($lastPos = strpos($html, $needle, $lastPos))!== false) {
    $positions[] = $lastPos;
    $lastPos = $lastPos + strlen($needle);
}
 
 ... while循环将在作业结束时结束...... 
 
$lastPos = strpos($html, $needle, $lastPos)
 
 ...返回false。 
 
 什么时候这个赋值会返回false？为什么？ 
 
 谢谢 

When would a PHP variable assignment return false?
 
In this answer the following code is suggested
 
while (($lastPos = strpos($html, $needle, $lastPos))!== false) {
    $positions[] = $lastPos;
    $lastPos = $lastPos + strlen($needle);
}
 
... the while loop will end when the assignment... 
 
$lastPos = strpos($html, $needle, $lastPos)
 
...returns false.
 
When would this assignment return false and why?
 
Thanks

原文：https://stackoverflow.com/questions/44574227